v.kernel - Generates a raster density map from vector points map.
Density is computed using a moving kernel. Optionally generates a vector density
map on a vector network.
vector, kernel density, point density, heatmap, hotspot
v.kernel
v.kernel --help
v.kernel [-
oqnm]
input=
name [
net=
name]
[
output=
name] [
net_output=
name]
radius=
float [
dsize=
float]
[
segmax=
float] [
distmax=
float]
[
multiplier=
float] [
node=
string]
[
kernel=
string] [--
overwrite] [--
help]
[--
verbose] [--
quiet] [--
ui]
- -o
-
Try to calculate an optimal radius with given ’radius’ taken
as maximum (experimental)
- -q
-
Only calculate optimal radius and exit (no map is written)
- -n
-
In network mode, normalize values by sum of density multiplied by length of
each segment. Integral over the output map then gives 1.0 * mult
- -m
-
In network mode, multiply the result by number of input points
- --overwrite
-
Allow output files to overwrite existing files
- --help
-
Print usage summary
- --verbose
-
Verbose module output
- --quiet
-
Quiet module output
- --ui
-
Force launching GUI dialog
- input=name [required]
-
Name of input vector map with training points
- net=name
-
Name of input network vector map
- output=name
-
Name for output raster map
- net_output=name
-
Name for output vector density map
Outputs vector map if network map is given
- radius=float [required]
-
Kernel radius in map units
- dsize=float
-
Discretization error in map units
Default: 0.
- segmax=float
-
Maximum length of segment on network
Default: 100.
- distmax=float
-
Maximum distance from point to network
Default: 100.
- multiplier=float
-
Multiply the density result by this number
Default: 1.
- node=string
-
Node method
Options: none, split
Default: none
none: No method applied at nodes with more than 2 arcs
split: Equal split (Okabe 2009) applied at nodes
- kernel=string
-
Kernel function
Options: uniform, triangular, epanechnikov, quartic, triweight, gaussian,
cosine
Default: gaussian
v.kernel generates a raster density map from vector points data using a
moving kernel. Available kernel density functions are
uniform, triangular,
epanechnikov, quartic, triweight, gaussian, cosine, default is
gaussian.
The module can also generate a vector density map on a vector network.
Conventional kernel functions produce biased estimates by overestimating the
densities around network nodes, whereas the equal split method of Okabe et al.
(2009) produces unbiased density estimates. The equal split method uses the
kernel function selected with the
kernel option and can be enabled with
node=split.
The
multiplier option is needed to overcome the limitation that the
resulting density in case of a vector map output is stored as category
(integer). The density result stored as category may be multiplied by this
number.
For the
gaussian kernel, standard deviation for the gaussian function is
set to 1/4 of the radius.
With the
-o flag (experimental) the command tries to calculate an optimal
radius. The value of
radius is taken as maximum value. The radius is
calculated based on the gaussian function, using ALL points, not just those in
the current region.
Compute density of points (using vector map of schools from North Carolina
sample dataset):
g.region region=wake_30m
v.kernel input=schools_wake output=schools_density radius=5000 multiplier=1000000
r.colors map=schools_density color=bcyr
School density
The module only considers the presence of points, but not (yet) any attribute
values.
- •
- Okabe, A., Satoh, T., Sugihara, K. (2009). A kernel density
estimation method for networks, its computational method and a
GIS-based tool. International Journal of Geographical Information
Science, Vol 23(1), pp. 7-32.
DOI: 10.1080/13658810802475491
v.surf.rst
Overview: Interpolation and Resampling in GRASS GIS
Stefano Menegon, ITC-irst, Trento, Italy
Radim Blazek (additional kernel density functions and network part)
Last changed: $Date: 2017-04-24 05:25:59 +0200 (Mon, 24 Apr 2017) $
Available at: v.kernel source code (history)
Main index | Vector index | Topics index | Keywords index | Graphical index |
Full index
© 2003-2018 GRASS Development Team, GRASS GIS 7.4.3 Reference
Manual